PURPOSE: To prevent the mutual interference to be produced between players by amplifying directly the variance of the capacity generated between the pit formed on a disc and the electrode of a pickup stylus with a high-input impedance amplifier, and taking out this variance as an output voltage.

CONSTITUTION: The variance of a quantity of electric charge, which is stored between pits formed on the disc and the electrode of the pickup stylus when a DC bias voltage is applied across the pickup electrode and the disc, namely, a variable capacity 13 is shown equivalently in a figure. A high-input impedance amplifier 14 having a source follower constitution consists of a field effect transistor FET15 and resistance 16, 17, and 18. The variable capacity 13 applies directly a variance accompanied with rotation of the disc to the high-input impedance amplifier 14, and this variance is amplified and is taken out as the output voltage from an output terminal 19.